1. Field of the Invention
The present invention relates generally to a multi-element metal chalcogenide and a method for preparing the same, and more particularly, to a multi-element metal chalcogenide adapted for being applied in a semiconductor solar cell, and a method for preparing such a multi-element metal chalcogenide. According to the present invention, the multi-element metal chalcogenide includes multiple metal elements. According to the method of preparing the multi-element metal chalcogenide, a powder of the multi-element metal chalcogenide is prepared, and all of the multiple metal elements of the multi-element metal chalcogenide are derived from simple substance powders of the metal elements, and/or one or more alloy powders mixed in accordance with a mole ratio. Then, a solution phase synthesis of the powder of the multi-element metal chalcogenide is conducted under the normal pressure to prepare the multi-element metal chalcogenide. The multi-element metal chalcogenide can be coated to obtain a film or used to make a target and then bombard the target for sputtering a film. In such a way, a selenization process which is conventional in fabricating the semiconductor solar cell is eliminated, thus improving the production yield and efficiency.
2. The Prior Arts
Copper-Indium-Gallium-Selenide (CIGS) solar cell was proposed by University of Maine in 1997, and the CIGS solar cell of that time has achieved a cell-efficiency of 6%. Up to now, it is known that a highest record of the cell-efficiency of CIGS solar cells is 19.9%, announced by the National Renewable Energy Laboratory (NREL) of the U.S. Department of Energy in 2008. Such CIGS solar cell not only has reached a high efficiency, but also can be stably used for a long time. As such, it is desired to be wildly applied in many different fields, including electric generation plants, or building materials.
“CIGS” of the CIGS solar cell represents Cu(In1-xGax)Se2, a major ingredient of an active layer of the solar cell. The active layer is adapted for absorbing sunlight and converting the energy of the sunlight into electric current. The CIGS active layer of the CIGS solar cell announced as having the 19.9% efficiency is a CIGS thin film having multiple metal elements of copper (Cu) indium (In), gallium (Ga), and selenide (Se). In accordance with a conventional method, such a CIGS thin film is fabricated by conducting a high-vacuum multi-source co-evaporation to deposit metal elements of Cu, In, Ga, and Se onto a substrate at the same time, while the substrate is being maintained under a temperature of 500° C. to 600° C. According to a principle of the high-vacuum multi-source co-evaporation, four individual evaporation sources of Cu, In, Ga, and Se are provided in a same vacuum chamber, and evaporated with individually controlled evaporation rates while the substrate is being maintained under a high temperature. In such a way, the Cu, In, Ga, and Se elements are simultaneously deposited onto the substrate, thus forming a CIGS thin film thereon. However, the CIGS thin film prepared by this conventional method usually has a low utilization rate, a nonuniform film thickness, and a nonuniform homogenicity. Further, the substrate is required to be maintained under a high temperature, and this adversely affects the production yield, increases the production cost, and restricts the production of large scale thin films.
In accordance with another method for preparing a CIGS thin film, a CIG thin film is prepared by bombarding a single target of a metal alloy containing Cu, In, and Ga (CIG alloy) or pre-depositing a metal precursor of a binary alloy. Then, the CIG thin film is disposed in a high temperature environment, and a Se vapor, a hydrogen selenide (H2Se) gas, or a hydrogen sulfide (H2S) gas is introduced to conduct a selenization or sulfuration process, thus obtaining a CIGS thin film. However, the selenization or sulfuration process is a complex and time-consuming process. It requires a high operation temperature, increases the process cost, and lowers the production speed. Moreover, it employs the highly toxic gas, H2Se, which requires a higher rank of security protection and corresponding protection cost.
In addition, for the purpose of improving the raw material utilization and production efficiency, and producing large scale CIGS thin films, other methods including electrodeposition, chemical vapor deposition (CVD), and spray deposition, had been proposed. However, these conventional methods are restricted by the unsatisfactory cell-efficiencies, raw material utilization, or crystalline thereof.
Even further, it has been found that ink-jet printing is an alternative method for preparing the CIGS thin film, and is adapted for improving the raw material utilization and preparing large scale CIGS thin films. Unfortunately, the cell efficiency of the CIGS thin film prepared by the ink-jet printing method is relatively low. In addition, the ink jet printing method requires to introduce hydrogen for reduction and to introduce H2S gas for selenization under a high temperature. Further, the crystalline of the thin film is usually not good enough, and the ink is not easy to prepare. As such, the ink-jet method is also not a proper one for alternation.
Furthermore, there are several methods for synthesizing CIGS nano-particles proposed as following.
Carmalt et al. proposed in Journal of Materials Chemistry 8: 2209-11, 1998, to prepare a CIGS thin film by conducting a solution phase metathesis synthesis with a metal halide and a sodium chalcogenide, and heating the precursor in toluene for 72 hours.
Further, U.S. Pat. No. 6,126,740, issued to Schulz et al. proposed to prepare a CIGS thin film by dissolving cuprous iodide (CuI), indium iodide (InI3), gallium iodide (GaI3), and sodium selenide (Na2Se) into pyridine, and having them reacted therein.
Further, Malik et al. proposed in Advanced Materials 11: 1441-4, 1999, a hot injection method for preparing a CIGS thin film. In accordance with the hot injection method, cuprous chloride (CuCI) and indium chloride (InCl3) are dissolved in trioctylphosphine (TOP hereinafter) to form a metal complex, and then trioctylphosphine oxide (TOPO hereinafter) is introduced therein, and then trioctylphosphine selenide (TOPSe hereinafter) is introduced therein for reaction, thus obtaining copper indium diselenide (CIS). However, this hot injection method can only obtain a ternary compound, and the obtained ternary compound even contains byproducts of cuprous selenide (Cu2Se) and indium oxide (In2O3) and is difficult to purify.
Pyrolysis is another known method for preparing a CIGS thin film, in which a (PPh3)2CuIn(SePh)4 metal complex is prepared at first, and then the metal complex is sprayed into a high temperature environment for pyrolysis therein and obtaining CIS powders.
Further, Grisaru et al. proposed in Inorganic Chemistry 42: 7148-55, 2003, microwave-assisted synthesis method for preparing a CIGS thin film. According to the microwave-assisted synthesis method, precursors including CuCl powder, In powder, and Se powder are dissolved in ethylene glycol, and microwave energy is then applied for pyrolysing the solution to obtain the CIS powder. However, the CIS obtained by such a process still contains Cu2Se byproduct and is still difficult to purify.
Furthermore, Li et al. proposed in Advanced Materials 11: 1456-9, 1999, a solvothermal method. According to the solvothermal method, CuCl2, InCl3, and Se powder are dissolved in ethylenediamine and diethylamine, and the solution is contained in an autoclave for reacting therein under a high pressure and high temperature for more than 15 hours, thus obtaining the CIS powder.
Still further, Jiang et al., proposed in Inorganic Chemistry 39:2964, to modify the precursors by substituting the halides of the with pure elements.
Moreover, Chun Y G et al., in Thin Solid Films 480:46-9, 2005, further proposed to synthesize Cu, In, Ga, and Se into CIGS powder with this method. However, this process is restricted by the reaction condition to be applied in a mass production.
In summary, all of the foregoing technologies have disadvantages. Some of them can be used for preparing ternary compound only, some of them require high temperature and high pressure conditions, while the products of some contains halide ions.
As such, it is highly desired to develop a multi-element metal chalcogenide adapted for being applied in a semiconductor solar cell, and a method for preparing such a multi-element metal chalcogenide. According to the present invention, the multi-element metal chalcogenide includes multiple metal elements. And according to the method of preparing the multi-element metal chalcogenide, a powder of the multi-element metal chalcogenide is prepared, and all of the multiple metal elements of the multi-element metal chalcogenide are derived from simple substance powders of the metal elements, and/or one or more alloy powders mixed in accordance with a mole ratio. Then, a solution phase synthesis of the powder of the multi-element metal chalcogenide is conducted under the normal pressure to prepare the multi-element metal chalcogenide. The solution phase synthesis can be conducted under a normal pressure, and does not require high pressure and high temperature operation conditions. The product does not contain any halide ions, and is adapted for mass production.